More Bad News About Grubee G4 Gearbox

Discussion in '4-Stroke Engines' started by Irish John, Sep 14, 2009.

  1. Irish John

    Irish John Guest

    After about a week of fairly low useage of the G4/HS kit described in another thread where I attempted to install it on a Grubee GT1 Cruiser bike I have to report that the freewheel drive sprocket has chewed itself to pieces. The pawls have ripped the ratchets to pieces carving through them like butter so in the end it freewheels in both directions and drives in neither.
    The problem is that the power take-up from the new belt driven G4 (this is the model without the engager) is too strong or the metal forming the ratchets in the outer cluster is too soft and the attached pictures clearly show the result of a about 130 kms of useage.
    This, added to all the other defects mentioned elsewhere, makes for a really disappointing experience of the total product.
    I'm not sure how this can be fixed and even if there is a non-freewheel fixed sprocket that might work (which I think there is) it has only 10 teeth and the problem with the GB is that the 11tT isn't big enough anyway. With a 10T front drive sprocket youd need something like a 24T rear and that is impractical for obvious reasons. The sprocket needed to match the 11T is a lot (and I mean a lot) smaller than the kit comes with. What the correct size should have been is something Grubee should find out for themselves because I do not feel inclined to tell them without being rewarded in some way that fully compensates me for the many too large sprockets I've had to buy with numerous kits to date.
    The G4 is really a back to the drawing board case.
     

    Attached Files:


  2. HoughMade

    HoughMade Guest

    As the self-appointed master of the obvious, I will state: That ain't good.
     
  3. jimraysr

    jimraysr Member

    G4 GruBee DEFECTIVE FREEWHEEL DESIGN

    The question comes to mind if the material the freewheel is made from would take a heat treat and become serviceable?

    Obviously something that would have to be done in the manufacturing process and not later in the field.

    I am guessing there is someone here who has the knowledge of the factors involved for such a process?

    I was also wondering if the freewheel from the older GruBee gear box is interchangeable with the one on the G4. Then is the material that same between them? I am not sure how you would test the strength of each part?

    Jim
     
  4. Luka

    Luka Member

    I'm betting that gear was either made from inferior metal, (probably a metal 'soup' of whatever they obtained the cheapest), or it was not hardened the way it should have been.
     
  5. fetor56

    fetor56 Guest

    Must be a weakness in their design or construction(or both) & from what's been reported the old freewheels arn't much better.
    Good idea by jim to see if there interchangeable,or get the vendor to replace it. :whistling:
    Either way certanly let the vendor know. :annoyed:
     
  6. jimraysr

    jimraysr Member

    Freewheel Problem With G4

    If it is the same,(freewheel) then it must be the torque delivery to it? As John indicated the driven sprocket must be smaller, that to me is an indication the output of the belt drive is not a high enough speed?

    Speed or torque, one goes down the other goes up every time. )

    Jim
     
  7. Irish John

    Irish John Guest

    George is replacing it but the problem remains - the 11T freewheel can't hack the increased torque that the belt drive delivers so it will chew through all 11T freewheel sprockets ad infinitum. The 11T is the same on all models as the pictures show.
    What is needed is a new sprocket design and while they are at it they need to get the gear ratio right because the current 11T & 44T is slower than the horrid old HTs and that is not what a 4-stroke is known for. A 4-stroke is about high cruising speed albeit with less pulling power from bottom to top speed. The fact that they boasted that this G4 can pull away up hill from a standing start is indicative that it was delivering more torque to the chain and the old 11T can't handle it.
    My most earnest advice to all the punters out there is to stick with the old Grubee gearbox because it works well and despite its noisiness it is infinitely better than the G4 will ever be in its current design.
    Terrible news about the 2010 Schwinn cruiser models. I've been too depressed to go out today. Why would they axe the very frame that won the 2009 Bicycling Magazine Best Bike - Editor's Choice yet still show the model and its accolades on their 2010 website when they have ditched that very frame? It beggars belief. I'll take a large dollop of my MPG Lithium Grease in a cup of tea because I'm told lithium help with depression.
     
  8. Irish John

    Irish John Guest

    G4 Clutch Bell is Tack Welded

    I was thinking that one way to reduce the torque on the 11T freewheel would be to try and get the three pole centrifugal clutch to grab at lower revs.
    Something similar to what Cheetoh invented for the old centrifugal clutches (see pics) and which really made a marked improvement in how the clutch grabbed and released the clutch bell. From attached pics it's hard to see where the 3 pole centrif clutch could be lightened by drilling. I can't see a way but someone else might have a great idea to contribute as happens on MBc.
    Why the clutch housing bell is only tack welded to the gearbox is beyond me but it looks very much like those JL Hoot engineers played a part in this.
    The G4 is so unready for sale that it isn't funny. My heart goes out to the stockists because it's not as if the manufacturer will pay for the expense of recalling them and resupplying the old GB for the duration of the 'back to the drawing board' phase of the debacle. They look like they'll get badly burnt but anyone who stocks up too heavily with an unproven Chinese product in preference to a proven one is a fool. This GB is really seriously problematic so be very carefull you guys who think it might be the answer to your problems,
    Incidentally in the Grubee picture the G4 has a fixed sprocket but it is the old 10T and that would exaccurbate the problem of the GB being already geared too low.
     

    Attached Files:

    Last edited by a moderator: Sep 15, 2009
  9. fetor56

    fetor56 Guest

    I had that clutch drum "tack weld" idea on my Titan PTO & it failed after 1 week of gently run-in.I was assured that this was a fluke & i was only the second person ever that this had happened to....not very assuring when your on the opposite side of the world.
    Tack weld is bad enough but chinese tack weld.......SHEESH. :rolleyes7:
     
  10. Irish John

    Irish John Guest

    Maybe able to use lighter springs instead of drilling holes.
     
  11. fetor56

    fetor56 Guest

    No matter what anyone sayes about the earlier Grubee tranny's their pretty strong.
    Lighter springs:You could try that & reduce the idle speed,BUT to my way of thinking since the new springs now engage earlier the whole setup will be under more stress(as the clutch shoes now more quickly engage with the clutch drum)
    Without physically seeing & playing with the components the problems you've described have basically been that of under-engineering....it's too weak.
    I goy my Titan PTO drum beefed-up with TIG welding & a replacement spare shipped free of charge(excluding freight ofcourse)
     
    Last edited by a moderator: Sep 15, 2009
  12. jimraysr

    jimraysr Member

    Chinese Pig

    It does look like they put lipstick on this pig?

    This clutch bell housing thing is old with them. Can't remember the box that had a pressed bell and they all cracked?

    It would look like the freewheel needs to be in the driven sprocket, but that would require them to actually engineer something original. I don't think there is one for them to copy out there large enough for the rag joint to fit inside?

    The whole width thing seems to be a non starter? Then the drive sprocket hanging out in mid air? Pretty disappointing.

    Jim
     
  13. Irish John

    Irish John Guest

    It would be less than honest not to say that the G4 is about as much use as t*ts on a bull!
     
  14. Hollbrow

    Hollbrow New Member

    Guys, I don't have one to study- but I am thinking of getting one. Can somone explain or point out the part that is tack welded to me please?
     
  15. Irish John

    Irish John Guest

    The centrifugal clutch expands as it spins faster to grab onto the clutch bell. The clutch bell is tack welded onto the bell housing rather than being either continuously welded or pressed into shape as a single piece of steel.
    My advice to you would be to stick with the superior older Grubee gearbox because the G4 is a much worse kit than its pedecessors.
    The top speed is way down on the G4 because they got the gear ratios wrong,
    It pulls away nicely but so would any GB with that ratio. As for its width well you will know what I've been saying when you buy one. Yes it is quieter but that's its only good point and most gearboxes are quiet at the sort of speed this thing crawls about at. I recommend giving the whole kit the elbow it so richly deserves Holbrow. There isn't a rear sprocket that fits it and the 11T drive sprocket will last a week before it disintegrates from the force of engagement that it isn't designed to withstand.
    At the moment there isn't a drive sprocket designed that works on it - it probably needs a 14T drive sprocket cos the 11T cetainly won't work unless you find a way of fitting a 36T rear sprocket that lets the chain pass all the obstacles that will be in its way.
    This gearbox will NEVER work as well as the older models and anyone fool enough to buy it will quickly find out this for themselves.
     
    Last edited by a moderator: Sep 17, 2009
  16. Hollbrow

    Hollbrow New Member

    I hear what you are saying- and I believe you Irish John. Looks as if the kit does have some serious issues, however, I see alot about it that I do like. (simple, quiet, lightweight). Aside from the tack welded clutch bell, does anything else appear to be wrong with the primary reduction set? Do the bearings appear adequate? Are there two bearings on the clutch bell shaft? That is probably what is making the whole thing be so wide- is getting enough room on that shaft to properly support it. The final drive from the primary down to the wheel does not concern me much- as I doubt I would use what came with the kit anyway. I'm used to starting from scratch with these things and doing whatever fabricating I have to. I would almost say that is a bad batch of really substandard freewheels that is stripping out like in those pictures- a good quality hardened freewheeel ought to stand what this rig will put out. Have you counted the # of teeth on the two belt pulleys in that primary? I'd like to know the actual ratio is to do some calculations.
     
  17. Irish John

    Irish John Guest

    The sprocket it needs on the drive shaft would most probably be too large to fit without hitting the engine casing. The 11T freewheels are not a bad batch cos I stock them and have a big supply from several batches. They are all badly made from soft steel and not made to acceptable cycling industry freewheel standards as I've said elsewhere. You'll get them to work on the old GB if you loctite the flange closed but the teeth will wear out at about 4000 - 6000 kms because the steel is so soft. They will not take the torque from this GB ipso facto.
    What the GB needs is to be designed to be thinner and the reduction ratio needs to be changed. By the time you do all this I can't see why you wouldn't fabricate your own gearbox from scratch so you get what you want.
    As for its weight advantage I can tell you that there is none - in fact it has to sit so high and with its excessive width you have serious balance and handling discomfort.
    There are probably a myriad of other problems that will show up in time because it was never tested anywhere else. I'm suspicious about the drive sprocket out on the end of that long shaft but how will it get tested when it won't go for anytime without the sprocket disintegrating? The only other sprocket that fits it is a rigid (non-freewheel) 10T but that makes the speed problem worse. I won't be wasting much more time on it but by all means buy one and spend an inordinate amount of time reaching the same conclusion. Without changing the reduction ratio you will get nowhere. Change the reduction ratio and you'll be making a working GB out of a huge ungainly monster that won't fit on a bike without making people laugh at you.
    You're flogging a dead horse when you sound like you could probably make a belt driven gearbox of your own from scratch.
     
  18. Hollbrow

    Hollbrow New Member

    Irish John- Ok- you make some really good points there. I have built several similar belt reductions from scratch- but with a slightly different twist. Instead of the clutch being directly on the motor output, I have done it before by going off the motor's output shaft
    with a belt pulley- to a larger belt pulley on a 5/8" jackshaft- then a regular comet 5/8 centrifugal clutch with a #35 chain on down to the rear wheel hub. This works surprizingly well as long as you have a freewheel on the bike hub so you aren't backdriving the jackshaft. I used a left handed freewheel on the heavy duty hub from Staton Inc. I took regular #35 two piece 'quick change' kart racing sprockets and machined an aluminum carrier plate that matches a shoulder on the freewheel- and use a backing plate to bolt the original freewheel teeth between to secure it. Doing that, I can change the sprocket on the rear hub to get any ratio I want within reason. The nice anodized sprockets look good too. My problem with the whole set-up is it too is a bit wide, making pedaling awkward, and the set-up is fairly heavy. What caught my eye about the G4 is the nice, compact, custom sized belt sprockets. Belt sprockets like those are VERY hard to find off the shelf in that pitch and those ratios- especially the larger one. I have hunted them so hard I would almost say they don't exist off the shelf. The ones I was forced to use are larger than I would have liked, and are made of nylon with an aluminum hub- and I still could not get them in the ratios I really wanted. They are also a square tooth design which is not as efficient as curvilinear. Can you possibly count the teeth on those G4 pulleys so I will know what ratio it is so I will not make a similar mistake?

    I think I'll take your advice and leave the G4 alone right now. I think they had a durn good idea- but ruined it by not doing all their homework. I really appreciate the info.
    Thanks.
     
  19. Luka

    Luka Member

    Is the steel CAPABLE of taking a temper, but it just hasn't been tempered ?

    Have you considered disassembling one, and tempering the thing, yourself ?
     
  20. Hollbrow

    Hollbrow New Member

    Irish John- just so I'm sure I understand, you're saying the G4 has TOO MUCH primary reduction- and that the chain sprocket on the output of the reduction box cannot be made large enough (and still fit) to get the ratio where it needs to be? I would really like to know how many teeth each of the belt pulleys in that reduction has- can anyone count them for me next time they get a chance?
     
Loading...